The demand for cellular and other multichannel wireless communications systems has led to development of broadband transceiver systems that are capable of processing many radio channels in parallel. While broadband transmission and reception of many radio channels in parallel through the use of sophisticated digital signal processing techniques provides an ultimate advantage of compact size and low price, this comes at the cost of more sophisticated, expensive, and sensitive radio equipment.
One such system component is the high power amplifier which must impart sufficient energy in the transmitted signal to close the communication link over distances of several miles to the mobile and portable subscriber units. Since the HPA is transmitting many channels in parallel, it must operate as linearly as possible, and impart as little distortion as possible in the resulting transmitted waveform.
For example, certain digital cellular protocols such as Global System for Mobile Communications (GSM) specify that the intermodulation distortion between adjacent channels must be at levels of -70 decibels (dB) or less.